High Voltage DC is used in several applications in industries, in equipments and Research. HV DC is also employed to transmit bulk power. That apart HVDC is used in testing of High Voltage Cables and as a source for charging the Impulse Voltage and Current Generator.

The most usual way of Generating High Voltage DC is through rectification using a) Half wave b) Full wave c) Multiplier Circuits. In all these cases the AC input is taken from a High Voltage transformer.

In a half wave rectifier, the rectifier unit which primarily consists of a set of diode (uni directional conducting devices), the conduction takes place during positive half cycle of the sinusoidal wave form only and it charges a capacitor which stores the energy. The circuit diagram is shown in Figure-1:

In a half wave rectifier, the rectifier unit which primarily consists of a set of diode (uni directional conducting devices), the conduction takes place during positive half cycle of the sinusoidal wave form only and it charges a capacitor which stores the energy. The capacitor too must be rated for the necessary High Voltage and the Peak Inverse Voltage of the rectifier unit must be 2Vmax where Vmax is the maximum voltage of the input AC wave. If the capacitor is connected to a load, then it slowly loses charge and gets replenished only in the next positive half cycle. The output DC voltage thus does not remain constant but fluctuates between a maximum value and a minimum value. The difference between the maximum and minimum value of the voltage is termed as ripple. Larger the value of the capacitor, lesser would be ripple. In addition the ripple voltage also depends on the frequency of the input AC voltage.

In this experiment, the HV DC rectified output from half wave rectifier is used to perform breakdown studies on symmetric sphere gaps.

Fig-2.Figure depicting Ripple

• To perform DC Breakdown studies on sphere gap of various diameters and gap spacing under varying atmospheric conditions.
• The AC input is derived from a identically rated set of transformers which are connected in cascade.

Simulation

1. When the page is loaded select the enabled Diameter from the 1st dropdown box for which corresponding gap distances are populated in the 2nd drop down box.
2. Experiment can be done for each gap distance in the given ascending order.
3. Specify the temperature and pressure in the corresponding text box.
4. Experiment can be performed only after entering the proper temperature and pressure values.
5. Click the setup Experiment button to perform experiment.
6. After triggering, the Experimental setup will be displayed.
7. Click the apply voltage button to begin applying voltage.
8. The red pointer on the knob is dragged towards right to increase voltage.
9. When breakdown occurs the knob movement will be arrested and the D.C.Breakdown voltage value will be displayed in the text box.
10. The procedure is repeated for remaining gap distances.
11. Upon Completion of Experiment for all gap distances a graph depicting the variations of breakdown voltage values and gap distances is displayed.
12. The experiment is repeated for available sphere diameters.
13. The overall curves depicting the variation of breakdown with gap distance for all diameters is displayed at the end.

Below are certain areas in which application of HVDC Test Source(Halfwave) finds its place:

• High Voltage DC power supply for Impulse Generators.
• Used for performing gap breakdown studies of various geometries.